The invention relates to a machining center for drilling, milling, lathing or grinding, comprising a swivel bridge supported between two bearing walls to be pivoted about a horizontal axis, at least one drive sprocket attached to a disc-type connector of the swivel bridge, at least one drive system attached outside to the bearing wall and operatively connected to the drive sprocket of the swivel bridge.
Modern machining centers for the cutting processing of workpieces by drilling, milling, lathing or grinding are increasingly provided with rotatable and pivotable workpiece tables. When using such a machining center, the workpiece may be brought into nearly any possible position by rotating and pivoting the workpiece table, without the need for releasing the initial clamping of the workpiece on the workpiece table. Therewith, nearly any possible solid angle at the workpiece may be processed in one workpiece clamping e.g. by drilling or milling.
In general, the rotatable workpiece table is arranged on a so-called swivel bridge for receiving the workpiece to be machined. The swivel bridge is usually supported on both sides and may generally be pivoted about a horizontal axis. However, also constructions in which the swivel bridge is supported only on one side are familiar.
When starting a machining cycle, the swivel bridge is pivoted into a predetermined angular position and then securely fixed in this position by a retaining mechanism. Only then the corresponding drilling or milling processing is performed at the workpiece. During the machining by drilling or milling, partially very large processing forces or moments may occur. Said processing forces or moments must be received securely by the retaining mechanism of the swivel bridge. Otherwise, the swivel bridge would be pushed away from the predetermined position due to the processing forces or moments. In addition, the retaining mechanism of the swivel bridge also have to provide a fail safe functionality. It has to be guaranteed that the retaining mechanism will also work in case of an energy breakdown, such that an unregulated pivoting or coast down of the swivel bridge due to gravity is excluded.
In EP 1 262 275 B1, a generic rotatable and pivotable workpiece table including a swivel bridge is described. The swivel bridge disclosed in EP 1 262 275 B1 is supported on both sides and can be pivoted about a horizontally aligned pivot axis. The swivel bridge is driven directly through its drive sprocket by a drive motor arranged outside at the bearing wall, such that there results a short force flow and no torsional load on the bearing pins. Retaining mechanism for the swivel bridge having a fail safe functionality are not disclosed explicitly in EP 1 262 275 B1. However, it is state of the art that the drive motor of a drive assembly as disclosed in EP 1 262 275 B1 is generally provided with an integrated motor clamping. Said integrated motor clamping operates on the basis of the permanent magnet principle, i.e. it is clamped in the electroless state. The ventilation of the clamping is performed electro-magnetically. When switching off the machining center (main switch OFF and machining center galvanically separated from the energy supply) or in case of an unexpected energy breakdown, the clamping hub is attracted by the magnet and therewith the motor shaft of the drive motor is retained. The motor clamping is also configured for a specific number of emergency brakings, i.e. for brakings during motion in case of emergency OFF or energy breakdown. A fail safe functionality of the retaining mechanism for the swivel bridge is therefore secured.
However, the motor clamping is not adapted and suited to retain the swivel bridge during the processing step in an angularly exact processing position. For this purpose, the swivel bridge of the present case has to be retained in its processing position by the position control of the drive motor. This quasi-electronic clamping guarantees the angularly exact processing position of the swivel bridge. In the present case, the retaining mechanism of the swivel bridge consists of two members: a mechanical motor clamping for the fail safe functionality in case of an energy breakdown or emergency OFF (emergency clamping or emergency braking) and an “electronic” clamping for the angularly exact positioning of the swivel bridge during the processing step (operation clamping).
The retaining mechanism for the swivel bridge disclosed in EP 1 262 275 B1 has the following disadvantages:
In order to maintain the operation clamping for the swivel bridge, the “electronic clamping” and thus the drive control of the related rotary axis must be activated partially for hours. This results in a considerable consumption of electric current.
Based on this state of the art, it is an object underlying the present invention to enhance the known machining center in that the operation clamping of the swivel bridge can be realized without the drive control and that the operation clamping is substantially free of clearance and can receive also largest processing moments securely and exactly, while maintaining the advantages thereof.
According to the invention, the object is solved by the following features:
A machining center for drilling, milling or lathing or grinding including a swivel bridge supported between two bearing walls to be pivoted about a horizontal axis, at least one drive sprocket attached to a disc-type connector of the swivel bridge, at least one drive system attached outside at the bearing wall and operatively connected to the drive sprocket of the swivel bridge, wherein the operation clamping of the swivel bridge is performed by a friction-locked clamping system which is arranged rotationally fixed about the bearing pin of the swivel bridge in a circular ring shape and is operatively connected to the disc-type connector, and that the clamping force of the friction-locked clamping system is generated by an energy storage.
Since the clamping force for the operation clamping is generated by an energy storage according to the invention, the drive control of the swivel bridge is not required for the operation clamping.
Since the friction-locked clamping system is further provided externally about the bearing pin, the largest possible diameter can be chosen for the clamping system. Therewith, the clamping system has a lever arm as large as possible and thus the largest possible clamping force.
Since the clamping system is directly operatively connected to the disc-type connector of the swivel bridge, a short flow of force results when clamping the swivel bridge. This is very advantageous for the static and dynamic rigidity of the operation clamping.
Preferred further developments and embodiments result from the sub-claims.
According to a preferred further development, the energy storage for generating the clamping force for the operation clamping consists of a mechanical spring energy store. A mechanical spring energy store can be realized particularly simply and is also inexpensive, since mechanical spring energy stores as a common machine member are available in any design. In addition, a mechanical spring energy store also does not need a large control effort to generate the clamping force.
As an alternative, the energy storage for generating the clamping force for the operation clamping may also consist of a hydraulic or pneumatic pressure accumulator.
Preferably, the mechanical spring energy store consists of a plurality of annularly arranged springs or of an annularly arranged, disc-shaped diaphragm which can be radially elastically deformed. Due to such a design, a large-scale clamping can be generated, which in turn results in a large clamping force.
According to a preferred embodiment, the friction-locked clamping system is provided with a pressure piece which is loaded by the spring energy store toward the drive sprocket. Such a pressure piece can transmit a large clamping force to the drive sprocket and therewith guarantees a secure clamping.
According to a preferred embodiment, the friction-locked clamping system for the operation clamping comprises a fail safe functionality such that, in case of an energy breakdown, the clamping occurs inevitably by the energy storage. Due to this construction, a fail safe functionality is integrated into the friction-locked clamping system, without the need for any additional mechanical mechanism. The clamping system thus has a double function: it clamps the swivel bridge in the desired position on the one hand, and on the other hand works as a fail safe device.
In order to guarantee a symmetric force transmission of the clamping force into the swivel bridge, it is preferred to arrange the friction-locked clamping system for the operation clamping on both sides at bearing walls of the swivel bridge.
According to a preferred embodiment, the friction-locked clamping system for the operation clamping is further formed as a radial clamping system shaped as a circular ring.
Therein, the clamping preferably occurs radially to the outside or inside, such that the pressure piece is pressed to the outside or inside during clamping.
Preferably, the circular ring shaped radial clamping system acts on the drive sprocket of the swivel bridge. Therein, the circular ring shaped radial clamping system preferably clamps outwardly toward the drive sprocket of the swivel bridge.
As an alternative, the circular ring shaped radial clamping system may also act on the disc-type connector of the swivel bridge.
In this case, the circular ring shaped radial clamping system preferably clamps inwardly toward the disc-type connector of the swivel bridge.
According to a preferred further development, the swivel bridge of the inventive machining center includes two independently effective clamping systems with fail safe functionality, i.e. a first clamping system formed by a motor clamping with fail safe functionality at the drive motor of the swivel bridge and a second clamping system formed by the clamping system with fail safe functionality at the bearing pins of the swivel bridge.
Further details, features and advantages of the invention result from the following description based on the drawings, in which: